Semiconductor films, such as silicon films, are known to be used for providing pixels for liquid crystal display devices. Certain prior art systems utilize line-type beams which are shaped to have a particular line-shape. An exemplary illustration of the line-type beam pulse 200, and a profile thereof are illustrated in FIG. 4A. In particular, the line beam pulse 200 may defined by a length L and width W′. The profile of the line-type beam pulse 200 illustrated in FIG. 4A has a convex top portion 205, a large section of which has sufficient energy density to be below a complete melting energy density threshold. This profile of the line-type beam pulse 200 also has a leading portion 210 and a trailing portion 215. The leading portion 210 has an energy density beginning from a low or negligible energy density level, continuing to reach a crystallization threshold, and ending below the complete melting energy density threshold so as to reach the convex top portion 205. The trailing edge portion 215 has an energy density starting from the edge of the convex top portion 205 (which is at a sufficient energy below the complete melting energy density threshold), passing the crystallization threshold, and ending at the low or negligible energy density level. The length L of the line beam can be between 10 cm and 50 cm so as to irradiate a significant section of a thin film provided on a sample. The conventional system generally use line beam pulses to irradiate the same section of the sample over 10 times with the energy density which is somewhat below the complete melting threshold. In this manner, a more uniform film may be attained, but the processing of such film is extremely slow. Indeed, the systems which use such line-type beam 200 are currently not suitable for quick processing of samples. In addition, when the edge portions (i.e., the leading and trailing edge portions 210, 215) irradiate the corresponding sections of the thin film, non-uniformity may be created in these sections.
As shown in FIG. 4B, other conventional systems attempt to overcome these problems associated with non-uniformity by continuously scanning display areas 220, 225 of the sample 180, until the entire area is completely irradiated. As shown in FIG. 5, this is generally performed by irradiating areas of the sample using successive pulses of the line-type beam 200, such that a significant portion of the area irradiated by a first pulse 300 of the beam 200 is subsequently irradiated by the next pulse 310. It follows that a sizable portion of the area of the sample irradiated by the pulse 310 is reirradiated by the subsequent pulse 320. Also, a large portion of the area irradiated by the pulse 320 is reirradiated by the next pulse 330, and so on. The overlap of the areas irradiated by the adjacent pulses is provided such that the distance between the adjacent pulses is the width of the top portion of the pulse divided by between 10 and 100, and preferably divided by approximately 20.
It may be possible to reduce the non-uniformity of the irradiated sections of the thin film sample by maintaining the energy density of the line-type beam pulse 200 to be above the complete melting threshold. In particular, as shown in FIGS. 6A and 6B, sections of a thin film sample irradiated at an energy density above the complete melting threshold 250 form small polycrystalline grains compared to sections of the thin film sample irradiated at an energy density below the complete melting threshold. Between these sections, there is a narrow region where grains are very large, due to near-complete melting of the film. In addition, when the energy density is below the crystallization threshold, the irradiated area is amorphous.
It is conceivable to reduce the non-uniformity of the irradiated sections of the thin film sample by maintaining the energy density of the line-type beam pulse 200 to be below the complete melting threshold. In particular, as shown in FIGS. 6C and 6D, sections of a thin film sample irradiated with beam pulses 200 at a constant energy density that is above the crystallization threshold and below the complete melting threshold 205′ have an approximately uniform grain size.
However, there are disadvantages to the use of these conventional methods. For example, when the irradiated areas of the thin film are required to be overlapped, the processing time of the entire sample is slow. This is because the sample is processed to ensure the reirradiation of significant parts of the previously irradiated areas of the thin film.